Power bank



FIG. 1 is a front, top, and right side perspective view of a power bank;

FIG. 2 is a front view thereof, the rear side being a mirror image thereof;

FIG. 3 is a top view thereof;

FIG. 4 is a bottom view thereof; and,

FIG. 5 is a left side view thereof, the right side being a mirror image thereof.

The broken lines present in the drawings are included for the purpose of illustrating portions of the article which form no part of the claimed design. 

CLAIM The ornamental design for a power bank, as shown and described. 